<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <script>
        var name = "World!";

        function adc() {
            let name;
            console.log(name)
            if (typeof name === 'undefined') {
                name = 'Jack';

                console.log('goodbye' + name)
            } else {

                console.log('hello' + name)
            }
        }
        adc()
    </script>
</body>

</html>